BillC wrote:
Is there a simple JDBC test to see if it connects? it is APEX_PUBLIC_USER who is connecting isn't it?

Yes - APEX_PUBLIC_USER is the connecting user.
You can use SQLPLUS to make sure you have the correct password.

After that, it is the SERVER, PORT, SID/SERVICE in the APEX listener you need to confirm.
You can TNSPING to confirm you have the correct selections for those.

You can always re-run the

java -jar apex.war setup

command to all of the basic settings.

The reason I mention that is because if you modify the settings manually - we need to ask "which file?" because there is the default and the database specific one too.

Try making a request to the service in standalone mode and you should get a terminal output (the window stays open) with a more detailed error. I would guess there will be an ORA-12514, TNS listener does not currently know of service requested in descriptor or something similar that will give you the "debug" information you are looking for.